1. Field of the Invention
This invention relates to a zoom lens system and an image pick up device having the same.
2. Description of the Related Art
Digital cameras, which are provided with a solid-state image sensor like CCD (Charge Coupled Device) or CMOS (Complementary Metal-Oxide Semiconductor), have become mainstream instead of film-based cameras in recent years. These digital cameras include various kinds of digital cameras which range from high performance-type digital camera for business to compact popular-type digital camera.
And, in such digital cameras, compact popular-type digital cameras have improved in downsizing because of desires that users easily enjoy photography, so that digital cameras which can be put well in pockets of clothes or bags and are convenient to be carried have appeared. Such small digital cameras can be stored in any space and used in any place, so that sturdiness and dust resistance also have become important factors for such small digital cameras.
Accordingly, it has become necessary to downsize zoom lens system for such digital cameras yet more, and, in addition, sturdiness and dust resistance have become necessary for the zoom lens system.
Zoom lens system which meet such requirements include a zoom lens which is disclosed in Japanese Patent Kokai No. 2007-286548. The zoom lens which is disclosed in Japanese Patent Kokai No. 2007-286548 is composed of a first lens group with negative refractive power, a second lens group with positive refractive power, a third lens group with positive power, and a fourth lens group. In this case, the first lens group always keeps still in changing a magnification. That is to say, the distance between the first lens group and the image plane does not change.